Asthma affects about 5% of the population in industrialized countries, and even more in developing countries. There is evidence that its evidence, severity and mortality are on the increase. Furthermore, the incidence of the childhood asthma is rising and there are suggestions of the link between environmental pollutants and the onset of the disease. Asthma is a controllable but not curable disease.
According to the WHO estimates 100 to 150 million people around the world are asthmatic and the number is growing by 50% per decade and causes 1,80,000 deaths a year. Asthma is a chronic, inflammatory lung disease characterized by recurrent breathing problems.
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People with the disease suffer ‘attacks’ or acute episodes, when the air passages in their lungs narrow and breathing becomes difficult. Attacks are caused by the airways over-reacting to certain environmental factors. For asthmatic people breathing becomes harder and may hurt—there may be coughing. The air may make a wheezing or whistling sound.
Two years ago, it was reported that one of every ten school going children in Delhi has been found suffering from asthma caused by the polluted air in Delhi. India has approximately 15-20 million asthmatics. About 50% of the patients visiting the OPD at the Post-Graduate Institute of Medical Research in Chandigarh are asthmatic. The climate of Bangalore, where the weather can change every two hours, gives it the dubious distinction of having the highest number of asthmatics in India.
According to Professor Duncan Geddes of the National Asthma Campaign, Britain, women who smoke during pregnancy are much more likely to have asthmatic children, and it is also linked with modern living—little ventilation, damp housing, more carpets and more dust. Initially bronchoconstriction—the narrowing of the airways in the lungs—was thought to be the most important feature of asthma.
Major risk factor for the development of bronchial asthma was considered to be atopy (a genetic propensity to allergy) and airways irritability. It is now recognised that inflammation in the lungs is an integral part of the development of disease. When an asthma sufferer inhales an allergen, their immune system effectively over reacts.
As a result of the various chemicals released, the blood vessels in the lungs become more permeable, allowing fluid to leak out. This causes a buildup of fluid which in turn causes inflammation. The chemicals also cause the smooth muscle cells in the lungs to contract. The result of all this is a narrowing of the airways. In addition, when white blood cells infiltrate lung tissues they also cause inflammatory damage.
Treatment of asthma consists of two main factors:
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i. Environmental control and
ii. Medication.
Environmental control means simply keeping away from factors—like tobacco smoke or allergens—likely to trigger an attack. Medication is the mainstay of asthma treatment. Because patterns of asthma are different for different people, the specific type of drug treatment varies a lot depending on the frequency, severity and particular triggers of each patient’s episodes.
For people with mild asthma, medication may only be needed before exposure to triggers or when they detect the onset of an attack. The major type of anti-asthma medicine are; corticosteroids, anti-allergy drugs and bronchodilators. Immunotherapy is also required where patient is desensitized to their allergens and can be useful where environmental control and medication have failed.
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Causes of Asthma Attack:
i. Allergens.
ii. Irritants in the air.
iii. Cigarette smoke.
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iv. Respiratory infections.
v. Too much exertion.
vi. Emotional stress.
vii. Sudden changes in weather.
viii. Certain medication.
There are two main sources of pre-formed or newly synthesized bronchoconstrictor agents in the lungs- mast cells, which are found in connective tissue and release histamine when stimulated, and macrophages found in the air sacs within the lungs. When the subject is exposed to allergens the immune system triggers the release of histamine from mast cells, as well as increasing the activity of the enzyme 5-lipoxygenase which produces leukotriene D4 (LTD4).
Now it has been proved that in patients with asthma, acute bronchoconstriction is caused by a mixture of histamine and LTD4. In the lungs of asthmatics there is population of allergen-specific white blood cells (T-helper cells) with a higher than average capacity for producing cytokines, which stimulate cells migration.
Cytokines, in combination with the locally generated exotoxin, stimulates a marked infiltration of lung tissues with a particular type of white blood cells, called eosinophils. These eosinophils are major contributors to lung inflammation because they release basic proteins which cause the damage to the lining cells in the airways during chronic asthma. There is also evidence for involvement of the nervous system in lung inflammation in asthma.
Warning Signs of an Impending Attack:
i. Light wheezing.
ii. Coughing pain.
iii. A tight feeling in the chest.
iv. Shortness of breath.
v. Restlessness.
The most straightforward way of dealing with the asthma attack is with a bronchodilator drug, which causes the airways to expand. The most effective bronchodilators are the β-adrenergic agonists, which are widely used and are simply administered to the lungs by portable inhalers.
In 1969, Ventalin was introduced which is an inhaled selective β2 agonist. A number of similar drugs including terbutaline, fenoterol, reproterol and pirbuterol have since been developed. The introduction in the early 1990s of the longer acting β-agonists salmeterol and formoterol is the most recent advance in this area.
Years ago when a severe hurricane hit the island of Tokelau in the South Pacific, the entire indigenous population was forced to move to New Zealand. On the Tokelau Islands, asthma was unknown. However, after the move, widespread incidence of asthma was noticed, especially among the children. This suggests that environmental factors have an important role to play in causing asthma- New Zealand has the world’s highest incidence of asthma (32%).
Environmental exposures and factors have been often associated with the onset of asthma, both in children and adults. Most environmental determinants of asthma are linked with changing lifestyles. Exacerbations have also been linked to air pollution levels, obesity, exercise, indoor smoke and exposure to environmental tobacco smoke and an affluent lifestyle.
Poor housing conditions such as dampness encourage the growth of moulds and house dust mites. These are known to be leading cause of asthma worldwide. Changing homes to areas where there may be larger concentrations of allergens is also known to exacerbate asthma.
A study by researchers at the Keck School of Medicine at the University of Southern California showed that children who play sports in areas with high levels of air pollution are three to four times more likely to develop asthma than other youngsters. The study involved 3,500 children ranging in age from 9 to 16 and having no history of asthma.
After five years, 365 children were diagnosed with asthma. Overall, the sporty children in high pollution areas were more likely to develop the disease. The research team is of the opinion that a high level of ozone is the main culprit as in low-ozone communities there was no increased risk of asthma in sporty children.
The consensus view of the current asthma therapy appears to be that we are well served with potent bronchodilators, which are best used whenever needed to reverse acute bronchconstriction. Bronchodilators like salbutamol are potent inhibitors of acute bronchoconstriction but there is little evidence that they have anti-inflammatory activity.
On the other hand, steroids are active in the inflammatory phase of asthma but do not have direct effects on airway dynamics. What is required is an alternative to the steroids which is safe, effective anti-inflammatory or immuno-modulatory agent which can be taken as an oral preventive once or twice a day in chronic condition.
For severe asthma, there is a group of patients who are steroid-resistant and here there is pressing need for treatments which modify the course of the disease. Current therapies treat only the symptoms of asthma, but new understanding in the field may lead towards the control of disease from its point of origin. It is hoped that new treatments also will be able to avoid some of the side effects associated with current therapies, such as water retention in the tissues or a generally depressed immune system.